Counting-relay selector and switching system



W n NN N 9m. ...nv e. n. 6MM M, J FH www m 2 n lm A TRM e C F G :L www fCX c o: N H4 J., J., J.,A mm w m, VMM a I Il N 7 m .m /Wwm Lm 2 L] NM AT P. e MM n m .wv R Dm. J. M w D l .Il m m DM N T .9 2 Gm, T 1H h V.Y l. m W Am. M m m H/ m E D w h. C fn L B Feb 20, 1951 Flled May 22, 1947 l. V. GRUNDIN ETAL COUNTING-RELAY SELECTOR AND SWITCHING SYSTEM Feb. 2o, 1951 4 Sheets-Sheet 2 Filed May 22, 1947 N Nm MM Mm JW MM WW MM An/ Z .NKONTQQWW bwk Feb. 20, 1951 1. v. GRUNDIN ETAL 2,542,079

COUNTING-RELAY SELECTOR AND SWITCHING SYSTEM Filed May 22, 1947 4 Sheets-Sheet 5 I R50! y"e502 R505 R *.k Tf il Pep. Rae/dg Se?l N92 Rp. Relay sez /99/ le R401 Kw2 Rm R40# @wf Rm 401 R408 R909 Rw@ Kw/ Rw@ Feb. 20, 1951 l. v. GRUNDIN ETAL 2,542,079

coUNTING-RELAY SELECTOR AND SWITCHING SYSTEM Filed May 22, 1947 4 Sheets-Sheet 4 Jupe/fan L l ne Patented Feb. 20, 1951 UNITED STATES N zene? COUNTING-RELAY SELECTGR AND SWITCHING SYSTEM Ivan Vitalis Grandin and Erik Gunnar Valfrid Erlandsson, Stockholm, Sweden Application May 22, i947, Serial No. 749,625 in Sweden December 11i, 1945 16 Glairns. i

This invention relates to communication systems and particularly to selector and switching systems for measuring, telephonie, telegraphic, radio or other communication purposes.

One object of the invention is to provide a switch or selector composed of relays provided with cores having a remanent magnetic field, which relays can be operated by means of short current impulses, and which has no other movable mechanical parts than the armatures and contacts of the relays. The selector is intended to be installed at a place at considerable distance from a controlling station or exchange and at which place there are no supervision and no current supply of any kind.

Another object of the invention is to provide a switching system particularly for telephone communication comprising a small automatic or semi-automatic telephone plant arranged to connect a plurality of subscribers lines over a few trunk lines to a supervisory manual or automatic exchange. Such a small plant is provided with a selecting equipment installed at a convenient place, for example in a sparsely populated district, in order to save the cost of long individual subscribers lines to a distant central exchange.

Switching equipment according to the invention can thus replace small manual switchboards, and an economic automatic telephone service can now be established between distant small telephone plants and a centrally located supervising telephone plant.

A switching system according to the present invention comprises selecting equipment consisting of one or more selectors, to which subscribers lines and trunk lines are connected at the local plant, and operating organs, for example a. repeating relay set for each trunkline installed at a supervisory station or exchange for the operation of said selectors at the said local plant.

Formerly it has been necessary to provide current supply of some kind at a distant small local plant for the operation of selecting equipment. Such a current supply, however, causes relatively high costs for installation, operation and maintenance.

In order` to avoid these disadvantages step-by step driven selectors, provided with rotatable contact arms, have been used. Such selectors are, however. exposed to wear and tear and often out-oi-order conditionsy occur. Such a selector calls for a relatively .high energy for its operation. In order to reduce the resistance of the trunk line through which the necessary impulse energy has to be transmitted, ground has been used as a return circuit, so that the potential drop in the trunk line could be reduced to half value. The use of ground as return circuit is, however, a great drawback, particularly from the view points of lightning, atmospheric disturbances and such potential differences, which always exist in the ground.

The present invention eliminates all of the above mentioned inconveniences and provides reliable selecting organs, which are easily operated with a minimum of energy.

A selector according to the invention comprises a plurality of successively operable electromagnetic relays, the magnetic circuits of which are so arranged that each relay, after having been operated by means of a current in a certain direction through a Winding of said relay, remains operated, due to 'a remanent magnetic leld in its core after the said current has ceased, and'means associated with the selector to direct a supplied de-magnetizing current to a winding of any of said relays for restoring the armature of any of said relays to normal position.

The remanent magnetic eld in the core is obtained by making the core of soft or mild steel.

After a current has caused the armature of such a relay to operate, the armature is kept in operated position, after the magnctizing current has ceased, due to the remanent magnetic field left in the steel core. A current impulse in the opposite direction through the Winding causes a magnetic :field in opposite direction. The said remanent magnetic iield is removed, so'that the armature returns to its normal position.

At least one selector according to the invention forms part of an automatic branch exchange in a switching system in which there are a plurality of stations, a metallic circuit communi# eating each station with said selector, a supervisory station, atleast one-metallic trunk line communicating said supervisory station with each selector. means at the supervisory station for transmitting current pulses over any of said trunk lines for operating and de-magnetizing any of said relays, in order tovestablish automatic communication between said stations and the supervisory station.

The invention will be better understood by referring tothe accompanying drawings, which illir-.strate selected ways of carrying the invention into effect, although it will be understood that the invention is capable of application to a number of different switching layouts, in which use is made or can be made of the inventive features set out in the accompanying drawings and claims.

measuring circuits over a trunk line to a superfvisory station.

Fig. 3 is a schematic diagram of` an automatic: telephone branch exchange comprising two selectors. to which exchange aplurality of subscribers lines and two trunk lines-to asuper-v visory exchange are connected.

Figs. 4-5 show a diagram of repeatingrelay sets and selectors at the supervisory station, which relay sets and selectors are connected overtrunklines with the selectors at the branch exchange shown in Fig. 3, andl also connected; overv junction linesof the samenumber asth'e subscribers? lines atthebranchexchange to the corresponding subscribersterminals at thesupervisoryexfchange.

According to the present invention. a: telephone switching system for the purpose above; indicated is composed of a telephone branch exchange without currentlsource land comprises a selecting device for each. of the' trunklinesto the super-'- visory station. These selecting devices: are com*- posed of electromagnetic relays,. which can. be caused to operate one after another byimeans'of current pulses over` a.v corresponding trunkline transmitted from the supervisoryn station and these relays thereafter remain operated by remato anv automatic branch exchange comprisingv selector` devices Sel. I and-Sel. 2. These selector devices are connected by metallic trunklines- Tr. I andfTr. 2 with repeating'relay sets I` and 2 at a supervisory station, which repeating relayv sets are connected bymeans of junctionY lines Je, J5

and J9 of the same number as the, subscribers connected to the branch exchange. 'I'hesupervisory exchange can bemanual, semi-automatic or automatic asfshown in the drawing, whereF is a finder switch and. Con. is a connector in. an automatic exchange.

l According toFig.V 2 connection canbe` established between a-supervisory dev-ice A at a;remo.te placeand` any oneoi ve.stations BI.-B5 con-.- nested to a. branch. exchange comprising, af select: ing device.'R2'I. R25. over. a. metallic circuit.. The,

supervisory device can consist, for example,.of aV measuring orcontrol device.. All stations. can also. be telephone. or. telegraph apparatuses, signal devices .or thelike.Y

The operation of the selecting device at the branch exchangel can be accomplished to a.. de.- sired position by transmitting short` current pulses ci' varyingdirection from the supervisory station by means of contact groupsV I 2 and 4 3 4 of relays R26 and R21 respectively. When relay R26 is actuated, current from a current source is transmitted over the trunkline Tr for a short moment, and relay R21 is operated at the branch exchange over a rectifier 2e and contacts 5 6 of relays R22-R25.

RelayRZI remains actuated on account of its remanent. magnetic field, after contact groups I 2 and 3 4 of relay RZ have been restored to; normal positions. In actuated position relay R2I keeps apparatus B connected to a trunlrline Troyer. its contacts I 2 and 3 4. By closing contacts I 2 and 3 4 of relay R28, station Bi can. be` connected to the supervisory device A.

IfV insteadstation B2 should be connected, contacts I 2 and 3 4 of relay R21 should be closed for ashort moment, whereby a current in opposite direction lis transmitted over the trunkline from the current source over a rectifying device 30, and relay R22 is operated over contact 1 8R2 I which was-previously closed.

As soon as R22 isoperated, relay R25 is oleenergizedlby the. same current pulse, which` operated R22, over contact 9 IlR22. Contacts 4R22. connect station B2 with the trunkline Tr.

By further current pulses of alternating direction. over contact groups I of relays R28. respectively R21 stations B3, Bl and B5 can be successively connected to the trunkline. After relay R25 has been operated by a current pulse over contacts I 4R2'6, whereby relay R24 is deenergized, the selecting device can be restored to normal by a further current impulse over contacts I IIR21'. Relay R25 is then de-magnetized by current over rectifying device 3Q and its own contact 1 8.

Inlig. 3 is shown a schematic diagram of a selector I associated with a trunkline Tr. i and ofA which relays RIDQ-RI I2 are provided' with remanent'magnetic field coresv of mild steel. A second selector'Z with trunkline Tr. 2 is she-wn in part with contacts in series with circuits conimon to the first selector.

Figures 4-5 show a schematic diagram oi a repeating relay set at the supervisory station. The i'lguresishow the equipment for a runkline Tr. I and the necessary contacts in the repeating relay'set No. 2Y for a second trunkline Tr. 2, which enterv in circuits common to the repeating relay set No. I. In the same manner as in Fig. 3 these common circuits can be extended to additional trunklines.

In the following a detailed description of the function of a' switching system will' be given follows:

(a) Outgoing calls from a subscriber at the branch exchange, Fig. 3.

(b) Incoming` calls to a subscriber at the branch exchange.

(0)* Interruption o1" a local call on account of an incoming long distance call.

(d) Restoration toY normal ci the switching devices after termination of a call.

(c) Supervision and time limiting devices.

(f) Automatic devices for marking and neutralizing out-oflorder conditions.

(g) Special details.

(a) Outgoing calls from a subscriber ctt the branch exchange (Figs. 3 5) Normally,.when noV call is made, relay R114 is operated over the trunkline Tr. I in series with windings of. relays R482 and Ri over the following circuit: Plus, winding R655, contact I 2R404, winding R402,.contact.3 R4III, upper wire of trunkline Tr. I, contact l-2RI I3, choke coil I2I, rectifier |22, contact Il-IZRIS, contact 1 -SR! I2, contact 8-9Ri i4, upper winding R! I4, contact ii-BRI I3, lower wire trunkline Tr. i, contact -IRM'IL lower winding R4Il2, contact 3-4R4il4, lower winding R4ll5, minus. The resulting current over this circuit will operate relay R4il5 and RI I4, but it is too weak to operate relay R402. Relays RI I4 and R495 are on account oi being normally operated shown with their con-- tacts in actuated positions in the drawings.

All subscribers lines normally pass over` break contacts of corresponding selecting relays of the two selectors to a common call circuit, which is connected to trunkline Tr. I when not busy. Only two subscribers Si and S2 are shown connected in Fig. 3.

The subscribers telephones are of normal common battery type with or without dial and a condenser in series with the bell. No current can therefore pass over the calling circuit, when all telephones are on their hooks.

If a subscriber, for example No. 2, lifts his telephone from its hook, current will flow over the following calling circuit and trunkline Tr. I: Upper wire of trunkline Tr. l, contact 2-3RI I4, rectifier lit, resistance i 29, contacts I-ZRZH, contact I-2R2Il2, rectifier I2I, contact 3 4RHl2, transmitter of subscriber S2, contact 3-4R2il2, contact l-2Riil2, contact I-2Ri I l, rectier il?, Contact -RI i4., lower wire of trunkline Tr. i. contact -lRlil, lower winding R42, lower winding R485, battery, upper winding of R435 and R492, contact 3-4R4QI, and back `over wires of trunkline Tr. I.

The current in the trunkline will now increase so that relay R452 will operate. When relay RME operates, a plurality of relays of the repeating relay set No. l will operate. Thus RME will operate, whereafter R486 and Riildi, which relays from a pulse transmitting device, will alternatingly operate and de-energize. Relay RME] will operate over the following circuit: Plus, contact -iR4il2, contact 4-5R4I2 resistance 45), winding R4H?, contact I-2R5I5, minus. Relay R11-14 will operate o-ver the following circuit: Plus, Contact EE-iSRi, contact I2-I3R4il5, winding R494, minus. Relay R435 operates over the following circuit: Minus, winding RMS, contact ii-lRt, contact -ilR4,!3, contact i-SRM i, contact 3-4R4El2, plus.

As soon as relay R453@ operates, it breaks its contacts 'l-i3, thus interrupting the operating circuit ofy R434, which de-energizes. When Riitl is de-energized, it breaks its contacts -l L and the operating circuit of R4il6 is interrupted,

whereafter the operation and cle-energization of these relays alternatingly will continue. Relay Ril-$4 thereby transmits current pulses over its contacts iof alternately opposite directions over the trunkline Tr. l. These pulses will cause each one of relays Rie-Rl i i of the branch exchange selector i successively to operate and to de-energize when the next relay in the chain is energized.

Synchronously with these operations of relays RIilEl-RI II relays R42-R43i! of a selector device associated with the repeating relay set No. l of the supervisory exchange are caused successively to operate and. de-energize in similar manner as above described for RIEIl-Rlli. These relays successively connect a number of junction lines (only No. 2 and 3 are shown in the drawing), equal in number to the subscribers lines connected to the branch exchange, and terminating in the switching organs of the supervisory exchange.

The operations are interrupted, when a calling subscribers line has been connected with the trunk line by the corresponding relay Rlll-RI i I.

The detailed switching sequence is as follows: Subscriber S2 lifts his telephone from. its hook and closes the calling circuit as before has been described. Relay 492 is energized. Relay M32 closes its contacts 3 4 and causes RME to operate as before described. Relay Rllii is somewhat slow-acting, due to resistance 45! and condenser 45 I. Relay R4IG closes its contacts I6I8 and I2-I3, whereby R429 and R454 are energized, the latter one being somewhat slow-acting. R429 operates over the following circuit: Minus,

winding R42il, contact I3-I4R4I2, contact ii-llR4il5, contact IiwiSRtill, plus. R434 operates over the following circuit: Minus, winding R404, contact l2-l3R4f`, contact Relay R4il4 changes the direction of current in the windings of relay R452 and in the trunkline T1. I and closes the following circuit: Minus, relay R403, contact Ii-3R44, plus. Relay R403 is energized.

When the said direction of current is changed, relay R492 and relay RII4 in the branch eX- change are de-energzed, because current through RI I4 is now blocked by rectifier 22.

When R433 is operated, contacts i-2 and 3--4R4ii3 are closed, whereby windings of R452 are shcrt-circuited, so that R4E12 cannot again operate after the direction 'of current in the trunkline is changed; The current over the trunkline is instead directed over rectifier I23 and relay Riil is operated over the following circuit: Lower wire of Tr, i. contact -llRiIS, winding Rice, contact -iiRl i I, contact l-2RIl2, rectifier i23, choke coil iZI, contact I-ZRI I3, upper wire of Tr. I.

When relay 402 is deenergized, its contacts 3-4 are opened, but relay Riii remains openated due to slow acting on accountJ of a condenser 45| connected in parallel with its winding.

When relay Ri i4- in the branch exchange is de-energized, the common calling circuit of the two selectors is switched over to the other trunkline Tr. 2, and a relay Rliz in the repeating relay set No. 2 is operated. Relay Rlil, however, does not operate due to the fact that its circuit is open by contact I9-2R4Ii.

Relay R493 closes the following circuit: Minus, winding R466, contact --lRi4, contact Ii-9R403, contact I-2R45, plus. Slow-acting relay R436 is energized. Relay R495 closes the following circuit: Minus, winding relay R4I2, contact I4-i5R4, plus. Slow-acting relay R4H is operated, whereby the previous energizing circuit of R42@ is interrupted, but relay R426 is kept operated over the following circuit: Minus, winding R4H, contact I-l IRA-2t, i5-i3R42 I, plus.

Relay R446 interrupts also the operating circuit of relay R464, which is de-energized after slow-acting. Relay RME momentarily interrups the operating circuit of R4!!! over its contact 4 5, which however receives operating current over its contact 8 E, contact SMQRAI i, contact 4--5R42, plus.

When R494 is de-energized, the original direction of current in the trunkline Tr. i is restored. Holding current for relay Rl G in' the branch eX- change is then interrupted, but Ri@ remains operated due to magnetic remanence of its core,

and directs; current from rectifier.l |22. to. relay;

Rl i2, so that relay R! l2 operates over the-fol'.- lowing circuit: Upper wire Tr. l', contact |'-2R.||3, choke coil |2|, rectifier i22, Contact lr-llRiil, winding RH2, contact -GRHS, lower wire Tr. i. At the same time slow-acting relay Ril is. de-energized, whenV contact G lRllil is opened. The time of release of Ril is'prolonged by means of a condenser 452 connectedV over the following circuit: Minus, winding Riil, contact 9-R!i5, contact i--iiRlii, contact l-iSRli, condenser 452, minus. Operating circuit of relay R433 is also interrupted, but the relay remains operated on account of slow-acting.

When relay Rlilt is de-energized, the following circuit is closed: Minus, winding RZi, Contact IQ--iB-ilRfiHi, plus, whereby relay R2| is operated. The operating circuit of RME is interrupted, out Rli2 receives holding current over theefollowing circuit; Minus, winding Rdi2, contact -i |Rfl|2, contact ill-IERG, plus, until relay Ra'i is operated, and thereafter it still remains operated due to slow-acting until its original operating circuit is closed again, as later on will be shown. Siow-acing relay R484 operates again over contact |2-|3R406.

Relay Rll! changes the holding current of relay Ri2al to the following circuit: Minus, coil RMB, contact |l-||Ri2i), Contact |5-|SR42|, contact iB-iQRiiS, contacts iE-|8-i'iR4|, plus.

Relay R-li again changes the direction of current over trunlrline Tr. The operating circuit of relay RE i2 ceases, but Ri i2 remains in operated condition due to the remanent magnetic field of its core. Relay Ridi operates due to current new received over rectifier |23 over the following circuit: Upper wire of trunkline TT. contact i-2Rii3, choke coil |2|, rectier |23, Contact 2-3Ri i2, contact l-5R|0, winding Rii, contact 5 RI i3, lower wire trunkline Tfr.

When relay R434 is again operated, the relays and Rdli successively operate againV so that the operating current of R423. is interrupted. Relay Rl2 is again operated, when relay R406 closes its contacts Iii-i5. ated over the following circuit: Minus, coil R42 contact l-idRflZL contact |6--HR422, Contact ii-l iiRi i 2, plus. il-l is de-energized after slow action.

When relay Rfi2 is de-energized, R4|3, which before was short-circuited over contacts |-2R420 and 2-3Rli i receives current over the following circuit: Plus, winding RMS, contact 2-3Rl|0, contact i-RiG, minus. Relay R4|3 is thus operated.

As before, Ri releases Rli. Relay Rll, when cie-energizing, reestablishes the direction of current in the trunkline Tr. l. The operating current of Ridi ceases in similar manner as before described, but remains in operated position due to its reinanent magnetic circuit. Relay Riil now receives current over rectifier |23, lwhereby it is (ie-energized. In the relay set No. the original operating circuit of R493 and RGQS are interrupted, but R503 remains in operated position as before due to slow action, and R406 is retained operated over another circuit as before described.

When relay Riill is de-energized, current is interrupted over the trunkline, and relay R405 RMI remains Opel'- 8l isl cle-energized. When R495 is de1-energizedre;- lay R496 is also cle-energizedv afterv slow'action;

When relay Rfiii' is de-energized, relayv R422 is energized over the following circuiti Minus; winding R422, contact ii-IZRZl, Contact 6-'iR42B, contact Il-ISRHS, Contactv |2- |3R4|2, contact i-ilR, contact l-BSR'MU; plus. R4i|3 is also cle-energized and relay R404 is operated.

Relay R422 switches the holding current of relay R22| which remains energized over |'3,- MRZI, i-lRllZE, i-IQRS, |5-|8-|'|R 4|0 to plus.

Relay Rtilfi again changes the direction'. of cur'- rent in the trunkline. Relay R|2 at thebranch exchange and relay Rli at the repeating relay set No. are operated. Relay Ri2 is operated in similar manner as before described with respect to Rii. Relays Rii and RME are again operated in the saine manner as before described, and Ri is released.

Relay R422 interrupts the circuit common to the two selectors at the branch exchange at its contacts |-2, whereby relay R'iiZ` is deenergized at the repeating relay set No. i. Relay R406 interrupts over its contact i-E'i the operating circuit of R522, but said relay Rli22 obtains holding current over the following circuit: Minus, coil Rl22, contact iS-iRfi22, contact |6- ilR-fl23, i-ISRMZL plus. Relay R223 operates, and relay Rfid-'1i is deenergized after slow action.

Relay Rii reestablishes upon its de-energizing the direction of current in the trunkline Tr. |v rl'he operating currentY of relay RiZ is interrupted, but remains in operated position, due to its reinanent magnetic field. Relay Rili' now receives current over rectifier |22, which removes the said reinanent magnetic field, so. that the armature of relay Riti returned to normal position. Relay Rl remains operated due to slow action, andrelay Rt receives holding current over its contact :-ii' as before described.

When relay Riili is Cle-energized, the circuit of the de-magnetizing current over rectier |22 is interrupted, but at the same time the trunkline T1'. iv is connected with calling subscriber S2. Current therefore continues to flow over the trunkline, and relay Riii continues in operated position, relay R686 is held in operated position as before, and Rlf is prevented from being operated, until relay Riils releases its armature.

When relay R is cle-energized from the pre- Vious release of Rili, the short-circuit of windings Ri?. ceases, and R432 is operated in series with R265. Relay Rdc@ is kept operated over the following circuit: Minus, winding Rlil, contact S-|Ri`s Contact iii- I iRfii, contact M-lR-i, contact Contact -ERM-I, contact S-fRili, plus.

Relay Rffi interrupts the operating circuit of relay Rii, which is cle-energized after slow action. When Rel@ is cie-energized, the operating circluit of Rfi is opened and Remi is deenergized. Relay Rfid? is operated andRlSl overA contacts S-Rf'iS, now closed, contactiS-RIZ,

contact 3 flRll2, plus. Relay RGIS now receives. holding current over the following circuit: Plus, winding RMS, contact -2Rl||i, contact -2Ril3, minus.

Relay R42? closes its contact |-2 and thus connects trunkline Tr. with junction line No. 2, leading to a supervisory exchange, which is now called over the following circuit: Current source at the supervisory exchange, lower wire of junction line No. 2, contact "-RZZ, contactv 1-3R4I3, contact I-2R402, contact I-2R401, winding 455 of R409, contact 4-5R4I3, contact -5R422, upper wire of junction line No. 2, line relay and battery at supervisory exchange. The current passing through winding 455 counteracts the current passing through the other winding 45S of relay R409, so that relay R409 does not operate. Relay R401 also closes the following circuit: Plus, contact 4-5R40'I, winding R4I I, contact Q lilR4I3, rectier 451, minus. Relay R4H operates.

The following relays are now operated: In the branch exchange: Rl I2 and RI 02: In the repeating relay set: R402, R40'i, R4I2, R422, R4I l, R4I3 and R405.

Subscriber S2 is now connected with the supervisory exchange. If this exchange is automatic, the subscriber receives a signal tone from the exchange, and he can now dial the desired num- Iber. The impulses are repeated in known inanner, when relay R402 breaks its contacts I-2, whereby the current in the junction line is interrupted and closed in step with the incoming dialed impulses. The disconnection of the established route is described under (d) (b) Incoming call to a subscriber atthe branch archange An incoming call to a susbcriber at the branch exchange is received over the junction line, which corresponds to the susbcriber at the supervisory exchange. The supervisory exchange is supposed to be automatic and so arranged that the a-wire of the junction line is coupled to the pluspole of t e current source of the supervisory eX- change, and that the b-wire is connected over a line relay to the minus-pole of said battery. All c-wires of the junction lines are in the repeating reiay set connected over rectiiiers and break contacts in some relays of the repeating relay set to a commen calling circuit 458. This calling circuit is coupled to relay R5I I, as long as same is idle. If it is busy, however, said relay R5I2 is operated and the call circuit is extended over the corresponding contacts of repeating relay set No. 2 to relay Ril i, if same is idle. In the following, it is supposed that repeating relay set No. 2 is busy7 and that repeating relay set No. l is idle.

The call circuit is thus connected to R4II of repeating relay set No. i.

When an incoming call arrives, the a-wire of the calling junction line is connected over a relay to minus, while the b-wire is connected to plus.

Relay R4li is then operated and afterwards Rlliii. Relay R4H is operated according to the following circuit: Minus at the supervisory excL-wire, contact 3-4R422, rectier 452, contact fla-4R522, contact 4-5R5i2, contact i-2Rfii2, contact 3-4R420, winding R-'ii I, con- ER-il, contact 5-tR403, plus. Relay Ril i operates. R4l0 then operates over the following circuit: Minus, contact i2R5iil, winding Rfli, contact l-BR4I2, contact 'i-3R4Ii, Contact 4-5R402, plus.

The pulse transmitting means, relays Rllt` and R444, start operating and transmit impulses or" alternating current direction over the trunkline.

Rite-Ri i@ of the branch exchange operate successively and simultaneously with selector device comprisingrelays R420-R430 at the repeating relay set. The operations cease, when that relay of Rem-R430, which corresponds to the calling junction line, has operated.

Relay Rfiiii then operates and signal current is transmitted over the trunkline to the desired tact ii--i 10 subscribers line over that relay of Ritt- Ri I0, which is operated in the branch exchange.

The sequence of operations for a call to subscriber S2 will be the following: Relay R4H opcrates and closes a circuit for relay Rllll, which also operates as before described. Relay R4i0 closes operating circuits for relays R42@ and R404, which operate, the latter one somewhat sloW acting.

Relay R420 interrupts the operating circuit of circuit R4I I, which is cie-energized. The operating circuit of R4l0 is then interrupted, but R4H) remains for some time energized, due to slow action on account of condenser 45 i Rel-ay R404 changes the direction of current in the winding of R402 and the trunk line Tr. I, whereby relay RI I4 of the branch exchange is cle-energized, and Rl00 is operated by current over rectifier |23y in the same manner as in outgoing calls.

Relay R403 is operated, when R404 operates as before described. Relay R403 closes the operating circuit of R406. R405 closes the operating circuit of R4l2, and interrupts the operating circuit of R404, which is de-energized after slow action.

Relay R4 I 2 closes the operating circuit of R4 I 0, which again receives operating current.

The sequence of'operations continues as previously described according to outgoing calls according to (a), until relay R422 is operated. Simultaneously with R422, R404 operates, whereby relay R02 at the lbranch exchange and relay R405 in the repeating relay set are operated. Relay R405 interrupts the operating circuit of R42I, which is fle-energized at the same time as R4I3 operates. R404 is de-energized after slow action, whereby RIOI in the branch exchange is de-energized. CurrentJ ceases in trunkline Tr. I and R405 is de-energized. The following operations will be somewhat different from those for outgoing calls.

rfhus R4I3 closes an operatingy circuit of R4I l, whereby this relay is coupled to the b-wire of the junction line No. 2. When the call, as supposed, has arrived over this junction line, said b-wire has plus potential from the supervisory exchange. R4H therefore operates over the following circuit: Plus at the supervisory exchange, wire bcontact 1-8R422, contact l-8R4I3, contact 3 4R401, winding R4H, contact 9-IOR4l3, rectifier 451, minus.

R4H closes holding circuit of R406. R404 is on that account prevented from operating again, and R403 is cle-energized. R4H also interrupts the operating circuit of R4I0, which is de-energized after slow action. During the slow action time limit, however, the operating circuit of R40I is closed and R4il| operates. R44! connects the trunkline over contacts 4-5R40I to the signal generator RG of the supervisory exchange, which generates alternating current of suitable frequency and voltage. At the same time R40I over its contacts I-2 connects a winding 435 to the tone signal generator SU of the supervisory station over the following circuit: Plus, tone signal generator SU, contact 4-5R400, contact I-2R4I0, winding 465R402, plus. As al1 windings of relay R402 are located on the same core, the tone signal is transferred over windings of relay R402 to the junction line 2 as a signal to the calling subscriber of the supervisory exchange, that ringing signal is being transmitted. Y

The signal generator at the supervisory exof R402 i iii change drives an interrupter INT, which intermittently connects terminal ISU to tone signal generator SU over contacts I-ZINT, and which intermittently connects terminal IRG to signal generator RG.

When RM@ is ole-energized, the operating circuit of R455 is interrupted and R456 is de-energized after slow action. The upper winding of R43! is then disconnected from RG and ccnnected over contacts S-'IRAGSL to terminal IRG for intermittent signal transmission. At the same time contact 2 of R46! is connected over contact S-Rii to a terminal ISU for intermittent tone signal and disconnects continuous tone signal over contacts l-SRli' from terminal contacts ReI-l. When Rei was cle-energized, the operating circuit of R40I was interrupted over contacts -lReIO, but RMI receives holding current over contacts I2-I3R4I3.

The signal alternating current passes in the branch exchange over windings of relay RHS in series with rectifying elements IIE-II6 so that RIIS operates. Relay RII 3 interrupts the circuits leading to the relays RIUi3-RII4 of the selector and short-circuits the rectiers II9 and |29 in the main circuit. The signal alternating current can now pass over the main circuit and the subscribers S2 bell. When the ringing current ceases, relay RI I3 is de-energized.

When subscriber S2 answers, direct current can freely pass over the trunkline Tr. I. As the signal alternating current in known manner is superimposed on the battery source of the supervisory exchange (the signal generator is coupled in series with the battery) direct current will pass over the trunkline, the subscribers telephone and the upper winding of RMI.

When RMI is de-energized, 4the signal alternating, tone-signalling and holding 'circuits of RISQI are interrupted. The trunk line is connected to the current feed relay R402, so that Ril and Rli are operated. R402 closes the operating circuit of Rkll. R691 when energizing closes its contacts I-E and 3--, so that upper winding of relay R499 is connected between the branches a and b of the junction line 2, and so that when the subscriber lifts his telephone from its hook, the answer is marked at the supervisory exchange organs by closing of contacts l-2R2- In the same 'manner as in outgoing calls, relay RMS receives current over its upper and lower windings in opposite directions, so that their magnetic 'fields counteract each other. The relay therefore continues vnonoperated.

'Ihe following relays Yare now Operated: In the branch exchange: RI I2 and RI02: In the supervisory station: R562, Rfid?, R4I2, R422, R4H, Rll and Rll.

Talking communication is now established over junction line No. 2 and Vtrunkline Tr. I to subscriber S2.

If both trunklines Tr. I and T1'. 2 now are busy, the common calling circuit of the repeating relay set is connected vover the following circuit to the transformer 458': Minus, one winding 'of transformer SESQ contact 4-5R5I2, contact 3-4R523, rectier 456, contact 3-R23, a-wire of another junction line, minus at the supervisory exchange. The other winding of transformer 458 is con- -nected to-busy tone generator B'I-Gfover thefollowing circuit: Plus, left winding of transformer 458', contact I-ERLIIL contact I-2R5II, busy tone .generator BTG, plus.

call, for example a long distance call In the supervisory exchange the junction'lines from the repeating relay sets terminate as ordinary subscribers lines connected to the said supervisory exchange. An established Vlocal call to or from a subscriber at the branch exchange canthus be interrupted in favour of a long distance call or the like to the same subscriber. The interruption takes place at the supervisory exchange in known manner. In such a case a time-limiting device, later on to be described under heading (e) shall, however, be restored to normal position.

A ringing signal shall also be transmitted to the subscriber in case he should have put his receiver on its hook. In order to indicate at the repeating relay set that interruption of an established call is taking place and to direct the necessary switching, relay R499 is used. When the interruption takes place, the current in wire a of the junction line is changed through the upper winding 455 of relay R405). The magnetic fields of the two windings 455 and 456 cannot counteract each other, and the relay operates for a moment.

Relay Rtli? closes the following circuit: Plus, contact 3-55R9, contact 5-6R433, which was closed by cam 4B I, when the local call was started, and winding RMI, minus.

Relay Rii which is a two-step relay operates its contacts :t only. Relay RllIQ is de-energized, and the following circuit is closed: Plus, contact -RliilL contact I-'2R4'3I, vcontact I-2R33, contact I-2 of self-interruptor R435, minus. The self-interruptor R535 then rapidly steps the cams IBI-453 to normal positions, whereby all contacts of R433 and .R534 are returned to normal positions, whereafter stepping relay R435 starts again, as if a new call should have time limitation. Detailed description of this tinielimiting device will be given in section (e).

If the subscriber at the branch exchange puts his telephone on its hook, when interruption is caused by the supervisory exchange, relays R452, R465 and RMS? are tie-energized, but relay RAI! is held in operated position. When relay Rlie operates, as above described, the following circuit is closed: Minus, winding RMI, contacts I-2R489, contacts -9R404, contacts 2-3R405, which is now cle-energized, plus. Relay Rel operates, and signal alternating current is again transmitted over the trunkline as before described in section (b).

If the subscriber at the branch exchange puts his telephone on its hook after relay R409 is de-energized after eiectuated interruption, relay RIDQ can be caused to operate again by connecting the signal alternating current circuits of the supervisory exchange to the junction line. On account of the relatively strong signal alternating current, which is rectied in rectiiiers associated with the upper winding 1355 of R459, the balance between the windings of RlIS is changed and Rs operates again and relay Rel is also operated, as has already been described.

(d) Return of switching devices to normal position after a terminated call During a call, one of relays RIIBI*RIII and RI I2 are operated at the branch exchange. In the repeating relay set No. I relays RME, R40?, R4I2, one of relays R4H-R435, Rell, Rl and R405 are operated. Clearing signal from the subscriber at the branch exchange is marked i3" by interruption of current in the 'subscribers line and thus in the trunkline. R432 and also R431 after slow action are de-energized. The holding circuit of R4H over contact 4-5R4'! to plus is changed to the b-Wire of the junction line over contact !-2R48.

If the other subscriber at the supervisory exchange has not given clearing signal, the said b-wire has plus-potential, and R4H is therefore kept operated. When, however, also the second subscriber gives clearing signal, the polarity of the potentialover the junction line is changed, and R4H is then fle-energized.

When relay R4i i is cle-energized, the operating circuit of Rlii is closed over contacts 8-9R4I2, contacts 8-3R4ii and contacts 4-3R432, plus, so that R4l4 is operated. Relays R406 and R434 then start successively to operate, causing successive operation and de-magnetization of R4H-R433 and Ri -Rl i3, as before described. When the last stage has been passed, relay R! I2 at the branch exchange is cle-energized and gives clearing signal to the repeating relay set, which signal causes all relays of said set to de-energize with the exception of R435. At the branch eX- change Rli4 is afterwards operated and relay R! ll is de-encrgized, whereafter the branch exchange and the repeating relay set are returned to normal. The sequence of operations and the circuits are similar to those established, when p the communication was set up.

( e) lSupervision and tiene-limiting device At the supervisory station and associated with each repeating relay set there is provided a device for the supervision of the calls and for the limitation of the time of each call. The device consists of a heat relay R433.l provided with bimetallic spring 2 between contacts l and 3, a two-step relay R43i, a relay R432, cam relays R433-434 and a stepping relay R435. The supervision of the calls is used in order to avoid blocking of the branch exchange on account of false calls due to shorteircuited subscribers lines or the like, and this is particularly the case, 'if the supervisory exchange is automatic. The supervisory device restores the exchange to normal position after a certain time, after a calling subscribers line has been connected, if no dial impulses have arrived during said time.

if, however, such impulses arrive, the device. is set to a substantially longer time, after which the exchange is restored to normal, if all trunklines are busy. The increased time limit is also set, when a callis made from the vsupervisory station to the branch exchange.

When the branch exchange has been set for an outgoingv call, and relay R401 is operated, it closes the operating circuit of thermal relai7 R433 over the following circuit: Plus, contact !!-i2R4il, bimetal armature 2 and contacts i-9R43i, contact 'i-SR43l, thermal winding R433, minus. After a number of seconds thermal relay R433 closes its contacts i-2, whereby the two-step relay R43i operates over the following circuit: Plus, contacts il-l2R41, contacts I-QRBS, Contacts 5-3R43i, Winding R43l, minus. In the first step all contacts marked at in the drawing are closed, while the other contacts are operated in the second step.

R43! interrupts the operating circuit of heat relay R436, and its bimetallic spring begins to cool off. When the said spring reaches its normal position and closes its contact 2-3R436, the following circuit is closed, if relay R432 at that time 14 is not operated: Plus, contact II-I2R41, con-iY tact 2-3R43B, contact !l.-!2R43!, contact 4-lR434, contactv i3--!4R43!, contact 3-4R432, contact 8-9R4l2, winding R4H), contact I-ZR- 5H), minus. Relay R4H) operates, and closes the operating circuit of R434, which operates. The branch exchange and the repeating relay set are restored to normal as described in section (d). Relay R4iili is then de-eenrgized and R43! is also de-energized.

If a subscriber at the branch exchange, after having been connected to the supervisory exchange according to section (o) dials a numeral before R433 closes the operating circuit of R4H), as above described, relay R432 operates according to the following circuit: Minus, winding R432, contact -eRAl, contact 43R432, Plus, because relay R432 is cle-energized a. number of times during dialling, and then closes its con-- tact 4-5. R432 receives holding current over` the following circuit: Minus, winding R432, con-- tacts Il-lZ-i R4H, plus.

lWhen R43! is operated in :is-position, R432 is' operated and when the bimetallic spring has cooled, relay R433 closes the following circuit:r Minus, contact 4-5R432, contact !3-i4R43l, contact '-LER4'34, contact li-I2R43l, contact 2-3R413i il-!2R4il!, plus. Upper winding of R43! is then short-circuited, and the relayl is de-energized.

When R43! is de-energized, the thermal relay R433 is again operated as before. After a few seconds it closes its contacts l-E and the first step of relay R43! is again operated. R43! closes operating circuit of R435: Minus, winding R435, Contact !-2R432, contacts 3 4-5-3-1 and S-liiR43i, bimetallic spring 2 of R436, contacts !!-'l2R40'!, plus. Relay R435 operates and turns cam shaft 454 one step. Contacts of R433 are then actuated. R43! interrupts the heating circuit of R433 and the birnetallic spring begins to cool again. After some seconds the operating circuit of R435 is interrupted and R435 is de-ener'gized. When R433 is restored to normal, its winding is again short-circuited and R433 is de-energized- The operations are repeated and the cams .of shaft 434 are turned step-by-step.

After a certain number of steps the contacts of R434 will be operated. Over its contact I- 2 a weak buzzer tone is connected to the winding 465 of relay R432 and transferred to the talking circuit. When the birnetallic spring has cooled, it closes the following circuit: Plus, !-!2R4!i'i, contact 2-3R43E, contacts i i-iZR- 43|, contacts 5-5R434, contacts i-2R5i2, contactile-QRMZ, winding R413, contact i-2R5i3 minus. It is supposed that R5i2 is operated in the other repeating relay set. RM@ operates and afterwards R434. R43? is (ie-energized and the selecting devices are restored to normal as previously described in section (d). During the restoration R4H is de-energized, whereby the operating circuit of R432 is interrupted and R432 is de-energized. When R434 was operated the following circuit was closed: Plus, ycontacts !l-,!3R44, contacts 5-5R433, lower winding R43I, minus. Relay R43l then operates its second step, and all contacts are operated.

Lower winding of R43l' obtains holding current over its contact le-i and 3-4R433- R43! also closes the operating circuit of R435 over the following circuit: Plus, contacts 4-liR4i9, contacts i-2R43i, contact l-2R433, contacts !-2R435, Winding R435, minus. Relay R435 breaks its own circuit, wherefore it def-energizes,

amatore operates again, and iso zforth. These operations Vcontinue until shaft 464 has brought -all cams to :normal positions, rwhere the `contacts of R433 are no longer actuated `by lits cam. When this operation is reached, the operating circuits Vof R435 are interrupted and .relay R43I is cle-ener- .jgiZeCL The same time limiting operations can take place for an incoming call. The only difference is that R434 immediately operates, when the selectors have been'operatedand vR4I I has closed the operating circuit of R432.

If a call vis interrupted in favour of another call, R403 operates according to (c). In this case -the lower winding of R43I operates both steps. When R409 thereafter is de-energized the Vself-interrupting circuit of R435 is closed, Aand the shaft 464 vand cams are returned vto normal positions as before described, while R43! is kept operated. When R433 Aand R434 have returned to normal position, R43I is de-energized, or returns to the first step, only closing contacts a2, depending vupon the position of the bimetallic spring `2R43t. The time limiting device then starts anew, as above described.

lf) Out-of-order'conditions If either of the .trunk lines are out of order due to line trouble, such as interruption, short circuit, the call circuits are automatically switched over to the other circuit. In the branch exchange this occurs, when relay RI i4 is de-energized, when the continuous current Aover `the trunkline ceases.

Relay RI I4 obtains holding current from the repeating relay set, when the satellite exchange is idle over the following circuit: Plus, upper winding of relay R405, contact I 2R4II4, upper winding relay R402., contact 3-4R4GI, upper wire of Tr I, contact i-ZRI I 3, coil I2I, r'ectier |22, contact II-IZRIEBI), contact 'I-ERI'IZ, contact 'I-8RII4, both windings RI I4, contact 5-6RI I3, lower wire of Tr I, contact 6-'IR40`I, lower winding of R442, contact 3-4R44, lower winding of relay R405, minus. Relay R405 is also actuated in the same circuit.

The common call circuit in the satellite exchange is connected to the trunkline Tr I over contacts 3 4 and 5-6RI I4.

If current over Tr I is interrupted, for example, if one of the line branches is interrupted, relay RIM loses its holding current and the relay is de-energized.

The common call circuit from the subscribers is then switched over to Trunkline 'T1' 2 over contacts I-2R i4 and 4-5RI I4 to vthe follow ing circuit: Plus, upper winding R532, upper break contact RSiiI, upper wire T1 2, contact 6-5R2I4, rectier ZI?, contact 4-5RII4, rectifier I I l, contact I-2RIII to contact I-2 relays RIill-RIIS, subscribers station, contact I Z relays REM-Zit, contact 2-IR2II, resistance I29, Contact 2-IRI I4, rectier 2I8, contact 2-3R2I4, lower wire Tr 2, lower break Contact relay R53i, lower winding R595, minus.

When a trunkli. e is short-circuited, R442 operates, and the repeating relay set is operated in the same manner as when an outgoing call is set up over junction line No. 2, as shown in section (a). The supervision device starts operating as described in section (e), and after a certain time the repeating relay set is returned to normal. If the fault remains, the selecting device remains connected to another junction line. and the sequence of operations are repeated..

Inithe meantime -RI I2 fisoperated .and keeps the y'call circuit A458 in E.the same condition as when the trunkline is busy. 'When the trouble is cleared, relay :R402 is zie-energized, and the switching vdevices are automatically restored as described in section (d), although in this case relays yRIE34-I I0 and R42*430 do not operate synchronously. The restoring operations are, however, terminated as described in section (d), when the branch exchange has returned to norvmal position, whereby the relays of the repeat- :ing.re`lay set are de-energized with the exception of R405. When the next call arrives, the operations take .place in normal manner.

(g) Special details .1. If the selectors of one of the trun'klines `during their operation must pass a position corresponding to a subscriber connected to the other' trunkline, the operation of the selectors should not be interrupted in said position. This might, however, happen, if special arrangements were lacking.

As previously has been described, relay R4I3 normally operates and is de-energized for each step of the selector relays. The operation of R4I3 facilitates the interruption of the selecting operation in the actual position of a selector by preparation of the circuits for holding of R436 and operation of R4'I I. The operating circuit of R4H is connected to the junction line which corresponds to a lparticular selecting step, over Contact 7 8 of a select relay R4H-R430, Contact E-B or l-8R4l3, contact 3-4R4Q`I, winding R4H., contact 3-IOR4I3, rectier 45?, minus.

When the selector passes a selecting step, in 4which .the .selector of the other trunkline is positioned (we suppose that the upper selector has select relay R522 operated), relay R443 is not energized, lbecause its winding is short-circuited over the following circuit: Plus, contact 6-5R5 I El, Contact -I-2R522, contact I-2R422, contact 2-3R4I, winding R4! 3, plus. The operating circuit of R4II is therefore not closed over contacts 6-1 or 'I-8R4l3. The selecting operation is therefore not stopped, when passing over voccupied selecting steps.

2. .If a subscribers line has been short-circuited and connected to one of the trunklines, it would be .impossible to apply va voltage to the corresponding selector relays, as these relays are conne'cte'd Yto the trunkline parallel with the subscribers line. It would therefore not be possible to Vdrive `the selector over said position. ln order to prevent the branch exchange to be blocked in such `a manner, the rectiers H9 and I2@ have been connected between the trunkline and the selecting contacts of the subscribers lines. The operating circuits of the selecting relays and their selecting contacts are so arranged, that the only operating impulse, which should be transmitted, while a subscriberfs line is connected to the trunkline, has such a direction that it is blocked by rectifiers IIS and IZB. This feature is olotained Yby the fact that each subscribers line upon voperation of the corresponding selecting relay is connected to the trunkline in series with break contacts of the preceding and the succeeding selecting relays.

A subscribers line is connected to the trunkline T1' I, when its connect relay (RISE) is operated and the preceding counting relay (RIII) is released. The preceding relay, for example RIUI, is released over the following circuit; Plus,

upper winding relay R405, contact |-2R404, upper winding relay R402, contact 3-4R40I, upper wire trunkline Tr I, contact I-2RII3, rectiiier |22, contact 4-5R||2, resistance |26, contact |'I-|0RI02, contact |3-|4R|0I, contact 6`IR|00, winding RIOI, contact E-'BRI I3, lower wire Tr I, contact E-'IR40I, lower winding R402, contact 4-5R404, lower` winding R406, minus. When relay RIGI is released, subscribers line S2 is connected to the repeating relay set over the following circuit: Plus, upper winding relay R405, Contact |2R404, upper winding R402, contact 3-4R40|, upper wire T1' rectiiier |20, contact 4-5RI02, subscribers station S2, contact 6-1R|0|, contact I0-9RI02, break contact RI03, rectiier IIS, lower wire Tr I, contact E-TR40I, lower Winding R402, Contact 3-4R404, lower winding R405, minus.

In order to step the selector, relay R|03 must be operated by changing the direction of current over Tr I. If subscribers line S2 is shortcircuited, and if rectiflers IIS and |20 were omitted, said relay RI03 could not be operated, because the wires of Tr I would be short-circuited over the following circuit: Upper wire Tr I, contact 4-5RI 02, short circuit between the branches of the subscribers line, contact 6-'IRIOI, contact I-0RI02, break contact RI03, lower wire TIT I.

If, however, rectiers H5 and |20 are connected as shown, relay RI 03 is not short-circuited for minus polarity over the upper wire and for plus polarity over the lower wire of Tr I, because the rectiiiers do not allow current of said polarity to pass over the subscribers line.

Relay RI 03 can, however, be operated over the following circuit: Plus, lower winding R405, contact 5-4R404, lower winding R402, contact 6-1R40I, lower Wire Tr I, contact 5-R|Iw, winding RI03, contact I3-I4R|02, contact II-I2RIOI, contact 4-5RI00, contact 2-3RI I2, rectifier |23, choke coil |2I, contact I--2RI|3, upper wire T1' I, contact 4-3R40|, upper winding R402, contact 2-3R404, lower winding R405, minus.

The selecting relays are besides so arranged that they operate for a direction of current contrary to that which is prevailing during conversation.

We suppose that subscribers line No. 2 becomes short-circuited. Said line will then call the repeating relay set, and the operations of the selector relays start as described in (a). When relay RI02 is operated, the subscribers line is not connected immediately, because the common circuit |30 is interrupted by R|0I, which is still operated. When the direction of current is reversed RIOI is de-energized, whereby said circuit |30 is closed, so that subscribers S2 line can'be connected to the trunkline Tr I. The selecting relays remain in the said positions, but the supervising devices of the repeating relay set No. I start operating as described in (e), and the impulse transmission is again started after a certain time. When the direction of current in the trunkline is reversed, the current over the subscribers line is blocked by rectiiiers |I9 and |20, so that relay R|03 can operate. This relay interrupts circuit |30 and the restoration to normal can continue. The short-circuited line will repeat the call, when the branch exchange has been restored to normal, whereafter the operations are repeated. Each time the selecting relays in said manner are operated, the selecting operations can be interrupted at 1S any of the other subscribers lines, if any of these are called. Thus the branch exchange cannot be made inoperative on account of short-circuited subscribers lines.

Conditions will be similar when a subscribers line becomes grounded.

3. The joint connection of all the subscribers lines in normal position, and the successive connection of same by means of pulses of alternate ing direction cause certain variations of potential in the subscribers lines. These variations might cause ringing of the subscribers bells. In order to avoid this inconvenience rectifiers II'I, II8, |21 and |28 are connected as shown in Fig. 3.

The rectifiers |21, |28 are individual for the respective subscribers lines. They prevent the discharge of the condensers' of the other subscribers lines in series with the respective bells,

when a call from one of the subscribers is made. i

Such a discharge would otherwise take place, as all the telephones are connected in their normal positions. The individual rectiers I2`I, |28, etc. are relatively small, so that they will not with a certainty prevent those discharges of the telephone condensers, which might be caused Vby the rst reversal of the potential over the trunkline after a call has been` made. Additional rectiers II'I and |I8 are therefore provided in both wires of the common call circuit.

4. When the selecting relays after a call are returned to normal according to section (d) and RI I4 is being operated, the common call circuit |30 is connected to the corresponding trunk line in parallel with winding of R|I4. If now a subscribers line is short-circuited, relay RI|4 would not be able to operate completely, but would be stopped, when it closes its contacts 3-4 leading to the common circuit ISI, unless special arrangements were made. The relay would then be de-energized and be operated again and so forth.

This inconvenience is prevented by means of a resistance |29 connected in circuit |30, and which prevents relay RII4 from being entirely short-circuited by the subscribers line.

5. When a call is arriving, alternating current is transmitted. This alternating current should not be allowed to disturb the selecting relays. In order to prevent this possibility, relay RI I3 operates and disconnects the selecting relays from the trunklines. happen, that a short but relatively heavy potential reaches the selecting relays, before RI I3 has had time to operate.

In order to prevent this, a choke coil |2| is connected in series with the operating circuits of the selecting relays, and a voltage dependent resistor, for example carbide of silicium, |24, is connected in parallel with said circuits.

When the alternating ringing circuit for calling the subscriber is transmitted over the trunkline, and before relay RI I3 operates, the counting relays are c onnected in parallel between the Wires of the trunkline over the following circuit: RG plus, contact 4-5R40I, upper wire Tr contact |-2RI |w, rectiiier |23, contact 2-3RI I2, and in parallel over contacts 3--4RI 00, I| IRIOI and make contact |3--I4 of the operated relay R|02, winding RI03, and over the resistor |24, which is connected in parallel with the counting relays; further over contacts E-BRI I3, lower wire of trunkline Tr I, contact I-8R40|, 'I8R406, RG minus.

Due to the fact that the resistance of the re'l It might, however,'

- 19` sistor |24 is substantially lowered, when subjected to high voltage of the alternating ringing current, only a small part of the said current will pass through the coil of counting relay RIUS. R|3 will not be operated by said current. The counting relays will however be operated by a lover voltage, when the major part of the current passes through the winding, in which case the resistance of the resistor |24 is high. For normal operating pulses the potentials in the trunk line will substantially appear over resistance |24 and the operating circuits. When a short and heavy peak potential, however, appears, a substantial part of the potential Will be absorbed in the choke coil |2| and only a minor part of the potential will reach the operating circuits."

6. When a call is `established in the branch exchange, one of the relays RlllI-l I8 and R1 l2 areV operated. If one of these should be deenergized due to undue mechanical 'or electrical action. the branch exchange can nevertheless be restored to normal by means of normal current reversal pulses. If therefore oneof RIUI-'RI I0 is ale-energized, 'a circuit is closed over the seriesconnected break contacts of all the selecting relays and closes a Vde-inagnetizing current 'circuit for R`| l2, so that it is vde-magnetized, whereafter the branch exchange-is restored to normal. When the repeating relay set shall restore the select organs, the selecting relays are stepped forward beginning with Rill!) according to section (a). The stepping continues until the normal position is reached, whereby the repeating relay set Ais also 'restored according to (d).

Ii vrelay R||2 is de-energized, when a call is established, said call is not interrupted. When the call in a normal manner shall be disconnec'ted, the stepping begins with relay RIOU, whereafter relay RI |2'can operate again. Due to the fact that the operating circuits of a selecting relay passes over break contacts of all preceding selecting relays, only one relay will be actuated at the same time, and the stepping therefore continues without difculty, until the normal position is reached." Branch exchange andv repeating relay set are thus returned to normal.

7. In the repeating relay set' there is a conidenser 45| connected in parallel with winding of relay R4H), whereby said condenser together with resistance' 45D in the operating circuit of relay Rdilca'uses a certain slow action. In this manner the selecting Aoperation is prevented from starting on account of so-called rapid instantaneous 'contacts between the wires of the trunk line, for example on account of swinging wires due to heavy wind.

8. In one of the operating circuits of relay Rl||| there is connected a rectifier 451, which prevents an unfavourable actuation of the relay by alternating signalling current', when lsaid relay is held over the b-wire of the junction line, and which alternating signal current might come over this wire from the supervisory exchange;

We claim:

l. In a switching system, a switching device, means at a'remote place including a direct current source and a pulse transmitting device for operating said switching device, a two--wire trunkline between'the switching device and said operating means, aV plurality of local lines con nected' to said switching device, said switching device comprising-a plurality of counting relays provided withk switching contacts for the ccn- 2.0.. nectio'n of said trunkline with any rof saidlocal lines, said pulse transmitting device comprising means to transmit direct current pulses from' said direct current 'source over both trunkline wires connected in series, means whereby said counting relays are automatically and successive ly operative and releasa'ble in accordance with said direct current pulses, a `circuit being provided between each counting relay and said trunk` line for the conduction'oi a direct current pulse to said relay for operating same and another circuit between said relay and said trunkline for conducting another direct current `pulse to said counting relay Yfor releasing same, said relay 'com'- prising means to keep it 'in'operated pcsition-be`- tween thev said operate and release pulses.

2. In a switching system, a 'switching device, means at a remote place including a 'direct cur' rent source and a pulse transmitting device for operating said switchingV device, a two-wire trunkline between the switching device and said operating means, a plurality of local' lines connected to said switching device, said switching device comprising a plurality of counting relays provided with switching contacts ior'vthel connection of said trunkline with any of said local lines, said pulse transmitting device comprising means to transmit direct current pulses from said direct current source over both trunkline wires connected in series, means whereby said 'counting relays are automatically andv successively connectable to said trunkline and selectively operable and releasable in accordance vwith said direct current pulses, each 'counting relay having a core and a coil on said 'cor'e, an operating circuit between the coil of each counting relay and said trunkline for the conduction of a direct current' pulse through said coil in V'one direction for operation of said counting relay, and another circuit between the said coil and said trunkline for conducting another direct currentv pulse through the said coil in the other direction for; releasing the said relay, the Vcore of said counting relay consisting of retentive magnetic material to keep said relay in operated position between' the said operate and release pulses.

3.' In' a switching system, a switching devil-ce, means',` at a remote 'place including a current source and a pulse transmitting device forv v:operating said switching device, a two-wire vtrunkline between 'the'switchirig device and said operating mean's, a plurality oflocal lines connected to said switching' devicasaid switch-ing device comprising' a plurality of" counting'rel'ays provided with switching ccntacts for the connection of said trunkline with any of said' local lines, said pulseftransmitting device `comprising means to 'transmit direct' current pulses from said direct' current source" over both tr'unkline wires connectedin series, means' whereby said coun-ting relays are 'automatically and successively connectable to`saidtrunkline' and selectively operative and releasable iny accordance with said direct current pulses', each counting relay being provided with a make contact, a core and a coil on said core, 'an operating'circuit between the coil'of each counting `relayand said trunkline for the conduction of a current pulse through said coil in one direction for operation of said counting relay and a releasing circuit between said coil and vsaid trunkline for conducting another direct lcurrent pulsethrough said coill in the other direction for releasing said relay, said releasing circuit passing over saidv make contact, the core of said counting relay consisting of re- '21 tentive magnetic material toA keep saidrelay in operated position between said operate and release pulses.

4. The switching system claimed in claim 3, in which a rectier is connected in series with the trunkline and with the operating circuit of said counting relays, and another rectifier is connected ,inv series with said trunkline and with the releasing circuit of said counting relays, and whereby said pulse transmitting device at the remote place comprises means to transmit direct current pulses of one current direction or of the other over said 'trunkline.' J

i 5. In a switching system, a switching device, means at a remote place including a current source and a pulse transmitting device for operating said switching device, a two-wire trunkline between the switching device and said operating means, a plurality of vlocal lines connected to said switching device, said switching device comprising a plurality of counting relays provided with switching contacts for the connection of said trunkline with any of said local lines, a two-wire main circuit in the switching device interconnected between said trunkline and said local lines and common to all the said local lines, said main circuit passing over said switching contacts of said counting relays, means in said main circuit to prevent obstruction of the correct function of said counting relays due to out-of-order conditions in any of said local lines, when coupled to the trunkline, said pulse transmitting device comprising means to transmit direct-current pulses from said direct current source over both trunkline wires connected in series, means whereby said counting relays are automatically and successively connectable to said trunkline and selectively operable and releasable in accordance with said direct current pulses, each counting relay having a core and a coil on said core, an operating circuit between the coil of each counting relayand said trunkline for the conduction of one direct current pulse through said coil in one direction for the operation of said'relay, and a releasing circuit between said coil and said trunkline for conducting another'direct current pulse through said coil in the other directionfor releasing said relay, the core of said counting relay consisting of retentive magnetic material to keep said relay in` operated position between the said operate and release pulses.

6. The switching system claimed in claim 3, in which a rectifier is connected in series with the operating circuit or said counting relays, and another rectifier is connected in series with the releasing circuit of said counting relays, said pulse transmitting device at the remote place comprising means to transmit direct current pulses of one direction or of the other over said trunkline, a choke coil being interconnected between said trunkline and said operating and releasing circuits, and a voltage dependent resistor in parallel with said counting relays, said resistor being of such a type that its resistance value is high when the resistor is subjected to normal operating potentials, and its resistance value is substantially reduced, when the resistor is subjected to potentials substantially higher than said normal operating potentials.

7. The switching system claimed in claim 3, in which the switching device comprises a switching relay connected to said two-wire trunkline, a two-wire main circuit interconnected between said trunkline and said local lines and common 22 to all the said local lines, said main circuit pass ing over the said switching contacts of said counting relays, said switching relay being provided with make and break contacts, over which said main circuit and said operating and releasing circuits are alternately connectable to the f trunkline, and means interconnected between said switching relay and said trunkline whereby said switching relay is operable by alternating current, and in which means are provided at said remote place for-transmitting alternating signaling current over said trunkline for operating said switching relay and for transmitting signals over any of said local lines upon the operation of said switching relay.

8. The switching system claimed in claim l, in which a two-wire main circuit is interconnected between said trunkline and said local lines and common to all the said local lines, each local line being connectable to the main circuit over break contacts in vcounting relays immediately preceding and succeeding the counting relay, which corresponds to said local line.

9. The switching systemr claimed in claim 1, in which a two-wire calling circuit common to said local lines and interconnected between said trunkline and said local lines is provided, a subscribers station connected to each local line, an individual calling circuit between each local'line and said common calling circuit passing over break contacts in a counting relay corresponding to said local line, a rectifier in each wire of said common calling circuit and an additional rectier in series with each individual calling circuit ior the prevention of false signals in the subscribers stations connected to said local lines, when the counting relays are stepped by pulses over the trunkline.

10. The switching system claimed in claim 1,

in which a two-wire calling circuit common to said local lines and interconnected between said trunkline and said local lines is provided, a resistance being connected-in series with one of the wires of said common call circuit for preventing blocking of the counting relays, should one of the local lines be short-circuited.

l1. The switching system claimed in claim l, in which a two-wire calling circuit common to said local lines and interconnected between said trunkline and said local lines is provided, at said remote place a line relay being connected to the trunkline for receiving a call from any of said local lines, means coupled to said line relay for starting the operation of said pulse transmitting device upon the receipt of a call, means in the switching device coupled to said trunkline and adapted to disconnect the said common calling circuit from the trunkline upon the start of said pulse transmitting device, and means at the said remote place for disconnecting said pulse transmitting device from the trunkline, when the calling local line has been connected by its corresponding counting relay to the trunkline.

12. In a telephone system, a branch oiice, a plurality of local subscribers lines connected to said branch oice, a supervisory office a direct current source and a repeating relay set including a pulse transmitting device at said supervisory oice, a two-wire trunkline interconnecting said branch oce with said repeating relay set, a two-wire junctor for each one of said local subscribers lines between said repeating relay set and said supervisory oiiice, said junctors terminating in said supervisory office as ordinary subscribers lines, said branch oice comprising 23 a plurality of counting relays provided with switching contacts for the connection of said trunkline with anyv one of said local subscribers lines, means whereby said counting relays are automatically and successively connectable to said trunkline and selectively operative and re.- leasable in accordance with pulses transmitted over both. trunkline wires connected in series with said current source, means whereby each counting relay is operable by one, current pulse and releasable by another current pulse, said relay comprising means to keep. it in operated position between the said operate and' release pulses, said repeating relay set comprising a selector connected to said pulse transmitting de- Vice, and meansv whereby said selector is selectively operable in accordance with the said pulses for connecting said trunkline to anyone of said junctors synchronously with the selectivev operay tion of said counting relays at said branch oce.

13. In a telephone system, a branch oice, a plurality of local subscribers lines connected to said branch oice, a supervisory oilce, a direct current source and a repeating relay set including a pulse transmitting device at said supervisory ofce, a two-wire trunkline interconnecting said branch oilice with said repeating relay set, a two-wire junctor for each one of said local subscribers lines between said repeating relay set and the supervisory oince, said junctors terminating in said' supervisory ofce as ordinary subscribensA line, said. branch cnice. comprising a rst selector for the connection of said trunkline with any of saidl subscribers lines, means whereby said selector is selectively operable in accordance with pulses transmitted over said trunkline from said pulse transmitting device, said repeating relay set comprising a second selector connected to said pulse transmitting device, and means whereby said second selector is selectively operable in accordance with the said pulses for connecting said trunkline to anyone of said junctors in step with the selective ope-ration of Said first selector at said branch oice for the successive connection to said trunkline of local subscribers lines at the branch oce and of corresponding junctors at .the supervisory oce.

14. A telephone system as claimed in claim 125, in which said repeating relay set comprises a relay for starting said puls-e transmitting device,

24 .a call circuit common to. said junction lnes:said junctors coupled to said startingA relay over said common call circuit, said starting relay being' provided, with means to vstart said pulse transmitting device upon the. receipt cf a call crer any of said j-unctors;

15. A telephone system as claimed in claim. 12, in. which said repeating relay set comprises: a relay for starting said pulse transmission device, a; call circuit common to said juncture a rectifier normally interconnected between each iunctor and the common call circuit. for preventing disturbing currents from one uncter to another, said conunon call circuit being normally connected to said starting relay which relay is provided with means; to start said pulse transmitting device upon the receipt of a call over any of said junctors.

16. A telephone system asl claimed in claim 12'.. in which said` repeating; relay set comprises a circuit common to said junctorsand normally connected to same, a busy tone transmitting device, and means for connecting said busy tone transmitting device, to saidV common circuit, when said selector is busy.

IVAN- VITALIS GRUNDIN. ERIK GUNNAR. VALFRID ERLANDSSON.

REFERENCES CITED.

Thel following references are of record in the le of this patent:

UNITED, STATES PATENTS N umser Name Date. Re. 16,293 Richardson Mar. 16:, 1926 961,342 Eastwoodv June 14, 1191-0 1,029,974 Burnham June 18:,y 1912 1,200,811 Clement Oct. 10:, 1916 1,374,201 Hall Apr. 12 1921 1,567,122 Dunham Dec. 29;,- 1925 1,886,216 Nilsson Nov. 1, 1932 1,992,389 Moser Feb. 26,1935 2,009,405k Leich July 30, 1935 2,019,320 Runner Oct. 29, 1935 2,054,702` Kiner Sept. 15, 1936 2,136,630 Massonean Nov. 156l 1938 2,260,810 Jones Oct.V 28,4 1941 2,297,092 Wicks Sept. 29, 1942 2,340,554 Peterson Feb. 1, 1944 

